The invention relates to a support material for recording layers which according to one embodiment of the invention may be a resin-coated support material.
Polyolefin-coated photographic support materials consist usually of a sized raw paper, which is coated on both sides with polyolefin, in most cases by extrusion.
With the extrusion coating of paper, crater-shaped faults occur on the polymer surface, as a function of the speed of the coating, referred to as pits. At high rotation speeds of the chill roll, the air bubbles which are enclosed in fine depressions on the surface of the chill roll cannot escape before coming in contact with the hot resin, with the result that the enclosed air does not escape until after the paper has been coated causing the formation of crater-shaped indentation on the polymer surface. These surface defects have a negative effect on the surface properties required of a support material, which are decisive for the image quality, such as gloss and smoothness.
An improvement in the surface can indeed be achieved by increasing the volume of the resin applied, but this measure is not sufficient at high extrusion speeds and also incurs high material costs.
EP 0 285 146 A2 proposes a gas for the suppression of the occurrence of pits, which is lighter than air and can escape through the extruded film, to be applied to the surface of the chill roll in order to expel the air bubbles. The disadvantage to this, however, is the high technical investment.
U.S. Pat. No. 4,994,357 proposes that the pressure with which the polyethylene-coated paper is pressed onto the chill roll be increased, to suppress the occurrence of pits. Because of the high contact pressure, however, only a low production speed is possible, since at higher speeds the polyethylene may come loose from the paper.
EP 0 952 483 A1 describes a photographic support material (base paper), of which the polyethylene surface is of high quality, and which is not impaired even by manufacture at high extrusion speed. To this purpose, EP 0 952 483 A1 proposes that the raw paper be provided with a layer containing clay, whereby the quantity of clay must not exceed 3.3 g/m2. The disadvantage with this support material is the inadequate adherence between the layer containing the pigment and the polyethylene layer extruded onto it.
A uniform surface of the support material is of significance not only for the photographic recording materials. To obtain an appearance similar to a photograph, polyolefin-coated papers are used in the manufacture of non-photographic recording materials, such as ink-jet papers. A non-uniform or blemished surface of the support material is made noticeable by glossy flecks on the recorded image, and is therefore also undesirable with these recording materials.